Curved structure



N. HART CURVED STRUCTURE Filed May 5,v 1941 VA. X A

MMM #uw l A14 we# Pat ated .lune il?, i944 CURVED STRUCTURE Norman Hart, Sutton, England Application May 6, 1941, Serial No. 392,112 In Great Britain May 9, 1940 1 Claim.

presses or the like, and Without stressing the material beyond its elastic limit, which structures are of the type (hereinafter referred to as the type escribed) comprising a plurality of pieces of resilient sheet material, joined together at curved edges of the pieces or parts, and adapted to be. used as envelopes, skins, containers and the like. y

Resilient structures having curved 'surfaces are required for a number of purposes, such as aeroplane and ships hulls, particularlyoi the highspeed type, seaplane floats, aeroplane wings, as well as fuel tanks, gun-shields and air-raid shelters, where it is desired to resisthpepeil'ltilfl, by proie es, vor damage by other impact, such mailing: grounding or stranding. It is recognised that a greater resilience or resistance to permanent damage can be obtained for a given material if the structure is supported or held in position by a minimum number of rigid members, thereby allowing a maximum resilient surface to absorb the shock of impact.

It is well known that boats hulls have to some extent, as in the case of ribband carvel constructions, been formed by a number of planks shaped to provide curved edges to t each other over,

in order that the completed structure having a curved surface shall be of the required shape curved both longitudinally and transversely, and cross timbers or stiieners are also required. Also, a similar steel construction has been employed, liough in this case the plates forming the curved surface were previously shaped by forging or other nie-ansto provide them With curved edges, and if released from their attachment would not return to their original flat shape, in other words they were shaped by mean which stressed the plates beyond their elastic limit.

It has also been proposed to form a resilient curved structure for use as a deck or part of the envelope of a boat from a piece of at resilient sheet material cut to form two symmetrical parts haring similarly curved edges which, in the flat, diverged one from the other, but which when joined together provided the required structure; when making this structure the two curved martrivial portions were stressed equally owing to the two curved edges being symmetrical, and to the joint being made by uniting portions of similar curvature.

An important object of the present invention is to provide a method of making improved structures of the type described of great resilience which automatically assume the required shape, without the use of moulds, frames' or the like, by joining together strips of at material having curved edges. Another object is to obtain a better controlled distribution of the stresses used to give initial curvature of the required structure than is obtainable by any of the methods of construction in. present use. Yet another object is to provide an improved curved resilient struc ture of the type described, in which the stresses determining its curvature are more easily contro-lied than heretofore, and which shall be more eiiicient than known structures of the same type and of a given weight in resistingpermanent damage and deformation. A further object is to facilitate and simplify the construction and manufacture of resilient curved structures oi the type described so that they can be readily made in large quantities and at a lesser cost than heretofore.

According to the invention, a method of con structing resilient curved structures of the kind described from iiat, resilient sheet material without the use of frames, moulds or the like, and without stressing the material beyond its elastic limit, is characterised in that curved borders of at resilient sheets, or parts of thc same sheet, are so shaped and so joined together edge-to-edge that the resultant structure automatically assumes a compound curvature owing to the 'vare ious stresses that are set up during the operation of forcing the curved borders to lie edge-to-edge and that are of diierent magnitude in the two sheets or the two parts of the same sheet. The term compound curvature used herein refers to a curvature in two directions lying transversely one of the other.

The invention also provides a method of constructing resilient curved structures of the type described comprising the steps of providing at resilient sheets, or parts of the same resilient sheet with curved edges and jo' together edge-to-edge in such" *celp'tin'ofa edge of one sheet, or a part thereof, is joined to a dissimilarly curved portion of an edge of an adjacent sheet or of an adjacent part of the same sheet. Consequently, non-corresponding parts of curved edges adjoin one another, and the resulting structure has imparted to it a compound curvature dependent wholly or in part on the difference in curvature of the edges at the joints in the structure, and the diiering stresses set up in the material at opposite sides of the joint.

Preferably, the` curves of those edges of the sheets or parts of the same sheet, which will lie at a joint in the resultant structure are parts of a definite curve as defined hereinafter. The term denite curve used-herein refers to a curve or arc, whereof the radiusv of curvature changes according to a predetermined equation. Examples of such de'linite curves are an ellipse, parabola., logarithmic spiral, catenary or sine curve, or a combination of such curves. Such a combination of curves may be composed of one definite curve, such as an arc of an ellipse that joins end to end to a second deiinite curve, whereof the curvature may correspond to the first curve, which curves however are arranged reversely one in relation to the other. One example of such a combination is a sine curve of 180.. Also, such a combination of curves may be composed of one definite curve, such as an arc of an ellipse joined end-to-end to an arc of a circle. Further, two spiral curves may be joined end to end, the one spiral having its curvature reversed in relation to the other, so that two spirals of opposite hand are joined together.

In some cases the edge of one resilient sheet to be joined to a second sheet may have the form ol' a closed curve, e. g., a circle, of one radius, and the edge of the second resilient sheet to be joined thereto may also have the form of a closed curve, e. g. a circle but or a smaller radius.

In order that the invention may be more clearly understood, a detailed description will now be given with reference to the accompanying drawing, in which:

Figure 1 is a plan view showing a plurality of strips of resilient sheet material all lying flat having curved lateral edges for use in making one form ci' resilient curved structure according to the invention, and

Figure 2 is a perspective view showing a resilient structure made by assembling strips of the lrind shown in Figure 1;

Figures 3 and fl show in plan and perspective view, respectively, another form of strip having curved lateral edges, and a frusto-conical structure made by assembling a plurality of such strips edge to edge; and 1 Figures 5 and 6 are views respectively corresponding to Figures 3 and l showing a Inodined form of strip, and a dished structure made therefrom.

Like reference characters designate like parts throughout the several I cvs.

Referring rst to Figures l and 2, a resilient curved structure of the type described, designated generally l2, for use as an enlfelope or skin of watercraft, or part thereof, isQerected from a plurality of ilat strips I4, l5, I6, Il, IS of resilber of similar reversed parabolic curves arranged extending in the saine general direction, but spaced apart one from another distances corre spondingr to the desired various widths of the strips to be cut from the sheet. As illustrated, the strip I4 is narrower than the adjacent strip l5,and the strip l5 is narrower than the two strips IS and VI which are substantially equal in width. After being cut, the strips are each of the shape, length, width and contour, that it is to have in the finished structure, and they are joined together edge-to-edge with non-corresponding or dissimilar parts of two adjacent curves joining one another. To do this and to ensure that edge-parts of like curvatures shall not be joined together, the strips while lying fiat and close together can be provided with marks at their edges, a mark on one strip being spaced away along the joint from a mark on the next adjacent strip to indicate a. part, e. g, at or near the end of one strip, to be joined to an adjacent part of the strip next adjacent thereto. After being moved endwise to bring the marks into register, the curved edges of the strips will not, while flat, lie wholly in contact one with another, but will have spaces between them. As illustrated in Figure l, each lower strip has been shifted endwise to the left hand in relation to the next upper strip, and the left hand ends of the strips have been trimmed along an end bounding line and placed one adjacent another at points des-' ignated 2U, 32, SL. on that line whereof the two end points are designated 353 and 3E.. In other v words, the strip l5 has been cut back at Si?, 32 a distance substantially equal to the distance between the point 38 and a point i351 on the curve ient sheet material, e. g. sheet. metal or wood, y

such as plywood, each having two curved longitudinal or lateral edges 2li, 22, which strips are to be joined together edge-to-edge in any convenient manner. The curvature" of the two lateral edges 20, 22 of all the strii s is the same, so that a description of one strip will sufce for all.

Referring to the strip I4, thecurve defined by its lateral edge 20 is a composite parabolic curve having two parts 24, 2S joined end to end at or near a point 28. The apices of these part-curves 2li, 2S lieadjacent to the lower and upper ends of the strip ifi as viewed in Figure l. Thus the curve dened by each lateral edge is a definite curve aforesaid, and the strips can be cut from a sheet of material by marking it with a num- 2i of strip it, the strip i6 has been cut back at 3?., 3i a greater distance substantially equal to the distance between the point 38 and a point 32 on the curve Eil of strip l, while the strip ll has been cut back at 34, S6 a still greater distance substantially equal to the distance between the point 38 and a. point i311 on the curve 2 of strip ill, and on the strip Il the point corresponds substantially to a point ISE on the curve 2li of strip lll. When these strips are placed on a at surface to lie as close together as possible, the adjacent curved lateral edges of the several strips will not Contact one another along their entire length. By bending the strips and forcing the non-corresponding or dissimilar parts of adjacent curved edges together and securing the joint 'thus formed, stresses of different magnitude will be set up in the strips, resulting in a resilient structure, which will have a compound curvature, as illustrated in Figure 2. This Figure 2 shows two sets of curved strips illustrated in Figure l, and an additional strip i8 of a similar kind, joined together to form a structure having a shape of composite curvature such as isrequired for the top sides of a ships hull. As illustrated, this structure is inverted lying with its lower part uppermost. In this structure the two sets of curved strips are joined together to form the bow at B along the line Sii-33 at one end of the two sets of strips, and at the opposite end at a line 4I to form the stern by cutting the ends of the strips to form a fair curve.

It will thus be seen that a feature distinguishing the known modes of construction of resilient curved structures of the kind referred to from that according to the present invention consists in that the curvature of the resultant resilient structure is determined by the described curved contour of the fiat sheets or parts of the same" sheet before they are joined together, and not by temporary or permanent moulds or frames used during erection.

The strips need not be of the same Width. The resultant sheet has parts of different degrees .of curvature in the transverse direction of the Strips, and the width of the strips may progressively decrease from a part of the resultant sheet -oi greater radius of curvature to a part of lesser radius of curvature.

The curvature of the edges of the strips joined together will in each case be such that when the strips are joined the elastic limit of the material of which they are composed is not exceeded.

An example of a strip whereof the width varies progressively is illustrated in Figure 3 showing a strip Gil of pliable sheet material that is bounded v laterally by two edges 52, 44 having each the form of a logaritl'imic spiral, whereof the centre is at 4t, about which a circle d8 is drawn. A plurality of such strips are provided, each terminating at its narrower' end 50 at an arc oi the circle 48. Il' a number of such strips are placed side-byside with the edge of one strip adjacent to the edge li of the next strip, a straight cone 52, as shown in Figure 4, or a part thereof, can be formed automatically by forcing the strips together at their edges and joining them together at the joints formed by the abutting edges. This is because when forcing the adjacent edges of the strips together, the strips are free to bend in a direction necessary for permitting the juncture of them one to another. This bending of the strips may give them a simple or a compound curvature, i. e.. a curvature in two directions lying transversely one oi the other. This compound curvature may not necessarily' be the same during construction asthat assumed by the material when all of the required adjacent strips have been joined together to i'orm one unit, partly because during the formation of the unitary structure the outer free edges of the strips are not then under stress that is due to their being joined to their adjacent strips. Also as the edges forming the joint between the two adjacent strips vary in curvature the amount of bending will vary as the joining up of the seam proceeds. This is true when making any structure provided by the present invention.

When in the final structure a strip would normaily have an outer edge that is not joined to another resilient strip, this outer edge may be stressed in a similar manner by applying to it a flanged ring, machined casting, a spun ring or. like suitably shaped rigid boundary member having an internal diameter less than that of the free outeredge of the structure by an amount which will assist in producing the required stress.

Referring to Figure-5, a strip 54 is shaped by drawing a centre line 55 in the form of a logmithmic spral having its centre at 58, drawing along the lne 55 circles 59, Bil, 6l, 62 of successively larger radius with their centres on the rentre line as indicated respectively-at 63, 84, G5, 56. and then drawing two fair curves at G8 and l0. each to bound one lateral edge of the strip, which curves terminate at one end at an arc 'l2 of a circle lli having its centre at 58. A spheroidal envelope of the lrind shown at l2 in Figure 6 can be produced automatically by joining a plurality of like strips 54 together edge-to-edge, .in the same manner as described above with reference to Figures 3 and fl.

In each of the constructions described above the entire boundary at an edge of the resilient curved structure, such as the top edge oi the structure l2 shown in Figure 2, or the bottom edge of the structure 52 shown in Figure 4, and the structure l2 shown in Figure 6, or part of the boundary, may be a rigid member, or a member having a greater rigidity than that of the said structure; for example, particularly in the case of hulls of watercraft, the boundary or part thereof may be a cast or forged stern plate, such as is commonly used to iorm the Bremen type bow. Also in some cases the resilient curved structure provided by the invention may be bounded Wholly or in part by a. rolled frame, such as an angle bar.

Various kinds of joints may serve for joining together the component parts of the resultant resilient curved structure. For example, single or double butt straps may be used. Also, Welding may be employed when convenient, and gluing may be used for suitable materials, as when a strip of wood, nbre-board, fabric. paper or the like, is to be placed at one or both sides of the joint in superposed relation thereto, and is to be secured in position by an adhesive. When butt straps or ribbands are employed they may have edges curved similarly to the sheets Which they are joining, or nearly so, in order to produce a similar transverse curve to that which is taken up by the strips joined by them. In this construction, the butt straps or ribbands will unc, tion in the same manner as the strips they serve to join.

If desired, a resilient curved structure that comprises a plurality of sheets joined edge-toedge may be cut from a resilient curved struc ture of the kind provided by this invention, such as is shown in Figure 2, Figure 4, or Figure 6. For example, the structure shown in Figure 2 may be divided into two parts along a line suoli as is indicated by the broken line 9S,

The invention thus provides various constructions of resilient curved structures as described above made according to the improved method set forth above.

I claim:

A resilient curved structure of the kind described rnade from fiat resilient sheet material without stressing the saine beyond its elastic limit, comprising a plurality of strips of the sheet material having marginal portions with curved edges joined together edge-to-edge with curved parts of an edge of one marginal portion of compound -curvature joined to curved parts of an edge of an adjacent marginal portion of different curvature, which parts in the final structure are curved in two directions lying transversely one of the other due tothe stresses set up in the material at opposite sides of the joints.

NORMAN HART. 

